Quarterly Financial Data (Unaudited) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011		Sep. 30, 2011		Jun. 30, 2011		Mar. 31, 2011		Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Quarterly Financial Data
Total Revenues	$ 47,738	$ 43,953	$ 36,885	$ 28,263	$ 29,457		$ 28,622		$ 21,566		$ 7,692		$ 156,839	$ 87,337		$ 29,057
Operating and maintenance expenses	20,086	20,541	16,566	15,576	15,666		13,857		12,418		12,361		72,769	54,302		50,277
Operating Income (Loss)	21,280	18,351	16,265	8,555	9,845		12,888		5,387		(8,011)		64,451	20,109		(34,001)
Net Income (Loss)	15,696	16,541	15,226	8,044	9,297		12,287		4,926		(8,011)		55,507	18,499		(34,001)
Limited partners' interest in net income	$ 15,334	$ 14,736	$ 12,721	$ 11,326	$ 11,314		$ 14,824		$ 7,738		$ 0		$ 54,117	$ 33,876		$ 0
Net Income per limited partner unit: (a)
Common - basic (dollars per unit)	$ 0.53	$ 0.55	$ 0.41	$ 0.37									$ 1.90	$ 1.11
Common - diluted (dollars per unit)	$ 0.53	$ 0.54	$ 0.41	$ 0.37									$ 1.89	$ 1.11
Common - basic and diluted (dollars per unit)					$ 0.37	[1]	$ 0.49	[1]	$ 0.25	[1]	$ 0.00	[1]		$ 1.11	[1]
Subordinated - basic and diluted (dollars per unit)	$ 0.30	$ 0.41	$ 0.41	$ 0.37	$ 0.37	[1]	$ 0.49	[1]	$ 0.25	[1]	$ 0.00	[1]	$ 1.47	$ 1.11	[1]

[1] Net income per unit is only calculated for the Partnership after the Initial Offering as no units were outstanding prior to April 26, 2011.